To manage electricity usage during times of peak demand, utility companies enroll consumers in load-management, or load-shedding, programs. Participants of load-management programs agree to allow utility companies to reduce their power consumption by controlling operation of the cooling or heating devices of their heating, ventilating, and air-conditioning (HVAC) systems. Control of such devices may be accomplished through the use of a controller integrated into, or cooperating with, a utility meter, thermostat, load-control device, or other such control device. In the case of cooling control, utility companies take control of compressors on some of the hottest days in an attempt to regulate peak demand for electricity.
Utility companies reward their consumers enrolled in such load-management programs with reduced electricity rates, rebates, updated equipment, and so on. These kinds of incentives may be effective in attracting a consumer to a program, but if a consumer's comfort is compromised, the consumer may drop out of the program.
Utility companies respond to this concern in a variety of ways. One way is to place limits on the control parameters. In one example, a utility company promises to limit the temperature rise during any particular control event, for example, four degrees. In another example, a utility company promises consumers not to control their system for more than six hours in any given day. Another more technological approach is to more precisely control the electrical load, for example, by cycling loads for shorter periods of time and allowing temperatures to rise slowly over time.
These top-down, utility-driven solutions, generally applied to residences, focus almost exclusively on control of a single device or load at a facility, namely an air-conditioning compressor or in some cases, a heating element. Further, absolute space temperature, or change in temperature, remains the measure of consumer comfort. Generally, such solutions do not attempt to control the circulation of air during a load control event, and generally neglect the effects that airflow, or lack thereof, may have on consumer comfort.
For example, in a traditional forced-air heating and cooling system, air is heated or cooled and forced through a network of air ducts by a circulation fan. Based upon a temperature set point, a thermostat calls for heating or cooling, and in the case of cooling, causes a compressor to turn on, and the circulation fan to circulate cooled air through the ductwork to various points about the structure, such as rooms in a residence, or offices in a commercial building.
When a load management system is introduced to the forced-air HVAC system, a load-management controller, often integrated into a thermostat, controls operation of the heating or cooling device to reduce energy consumption. With some load management techniques, the temperature set point may be modified, for example, by implementing a slow temperature ramp-up so as to not call for cooling. With other techniques, power to the energy-consuming appliances may be cycled on and off to control both temperature and energy usage.
However, known load-control, or demand-response, thermostats and other load-control devices generally do not take into account control and operation of the circulation fan during a load-control event. The earliest known load-control thermostats simply left the circulation fan off during load control events. In some devices, this is a relatively simple operation, as a circulation fan often tracks operation of an air-conditioning compressor, turning on when the compressor is powered on, and off when the compressor is off. Some later-developed thermostats allowed for a circulation fan to be turned on manually by a consumer via the thermostat.
For example, U.S. Pat. No. 4,382,544, entitled “Energy Management System with Programmable Thermostat” to Stewart (“Stewart”) discloses a user-programmable thermostat that controls furnace and air-conditioning units as part of a load-shedding program. Stewart discloses that the thermostat controls temperature through control of the furnace and A/C, but control of the circulation fan is left to the user which may manually turn on the fan during a load-control event if desired. In another example, U.S. Pat. No. 4,345,162, entitled “Method and Apparatus for Power Load Shedding”, the circulation fan is simply turned on during a load-control event.
Unlike the top-down, utility-driven solutions described above, some bottom-up, consumer-driven solutions, generally commercial, implement sophisticated control schemes to control more than just the heating and cooling elements of an HVAC system. In such systems, a circulation fan may be treated as just another electrical load to be cycled for energy management purposes, with little or no consideration given to its effect on consumer comfort.
As such, known devices and methods for controlling electrical loads, especially heating and cooling loads of an HVAC system, fail to coordinate control of circulation fans during load-control events, and thereby fail to maximize potential comfort of the consumer.